The moving voice coil/diaphragm type transducer configuration has been utilized widely in loudspeakers, where the main moving diaphragm is typically but not necessarily conical in shape with its inner edge attached to a voice coil bobbin. Typically there are two resilient suspension members: a spider attached to the voice coil bobbin generally near the region where the bobbin is attached to the cone, and a surround member forming an annular border strip having its inner edge attached around the outer edge of the cone and its outer edge attached to a peripheral flange of the speaker frame. Both of these suspension members are required to provide the cone/voice coil assembly with elastic freedom to move back and forth over large excursions along the central axis while at the same time providing sufficient lateral stiffness to hold the voice coil and bobbin concentrically aligned within the gap between the magnetic poles.
It is quite difficult to find suitable materials that will act satisfactorily as suspension members in a hostile environment such as an automotive exhaust pipe where the temperature can range from -40 to +600 deg. F. (-40 to 316 deg. C.), compared to a much narrower range, typically 0 to 150 deg. F. (-18 to 66 deg. C.) over which ordinary loudspeakers are designed to operate.
For this severe duty, generally most materials will be found unsuitable in either fatigue endurance, acoustic properties or flexural properties, when subjected to extreme heat and cold.